2404
NOTES
I
100
/:;
a
I
A
I
200 300 T I M E AFTER SHOCK REFLECTION (piset)
e-
and Sadhan K. De Chemistry Department, Indian Institute of Technology, Kharagpur, West Bengal, India (Receiued February 1 , 1971) Publication costs borne completely by The Journal of Physical Chemistry
J
400
reactions. lo The initial concentration of chain carriers, (0H)o in the above example, is linearly proportional to the initiation rate.I0 I n the present study it has been found that the exponential growth constant is not affected substantially, but the reaction time is greatly reduced in the presence of Cr(C0)G. From these observations it can be said that Cr or some species containing Cr is not involved in the main chain branching reactions but enhances the chain initiation process. It could be suggested that the Cr compound(s) form some activated complex with C2Hz which produces chain carriers either by reaction with O2 or by thermal decomposition. The activated complex of the type Cr(CO)S(C2Hz)as suggested in the flash photolysis systemj3however, is not probable a t all, because under the present experimental conditions the decomposition of Cr(C0)G is known t o be very fast.4 I n the shock-tube study of the Cr(C0)6-Qz and Cr(CO)G-CO-02 reaction systems by a time-of-flight mass spectrometer, the formation of CrO, Cr02, and Cr03 is ~ b s e r v e d . ~Therefore, it seems more likely that Cr atom formed by the decomposition of Cr(C0)s is oxidized to CrO, CrOz, and CrOs in the present reaction system and the CrOB(or Cr02)reacts with CzH2to form chain carriers. Since a very low concentration of Cr(CO)Gis used in the present study, the possibility of solid particle formation (chromium oxides) is completely eliminatede4 Acknowledgments. The authors gratefully acknowledge financial support from the donors of the Petroleum Research Fund and from the National Science Foundation. The authors wish to thank Professor G. B. Kistiakowsky and Dr. T. P. J. Izod for their helpful discussions. K. Bradley, Trans. Faraday
Sac., 63, 2945 (1967).
The Journal of Physical Chemistry, Val. 76, N o . 16,1971
by S.Mukherjee, S. R. Palit,* Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-S%, India
Figure 2. Plots of emission intensities vs. reaction time from two oscillograms shown in Figure 1. The exponential growth constant calculated is for (a) 3.35 X 104 sec-’ and for (b) 3.20 X lo4 sec-’.
(10) J.
a Hydrogen Bonding
A
A A
N-H . .
Although hydrogen bonding of hydroxylic compounds (that is, phenols and alcohols) with P-electron systems of olefins and aromatics has been studied by various workers in the recent year^,^-^ there has been but little investigation on N-H . a-type hydrogen bondingaG This note presents the results of our investigations on the hydrogen-bonding interaction where N-H of anaphthylamine acts as proton donor and n-electron systems of aromatics act as proton acceptors. We have utilized Nagakura and Baba’s suggestions that a-a* transitions of organic molecules with suitable chromophores undergo a red shift in proton-accepting solvents due to solute-solvent hydrogen-bonding interaction and also spectral measurements at the shifted peak can be used to evaluate the equilibrium constant for the complex formation.’
-
d8
Experimental Section The a-naphthylamine (B.D.H.) mas recrystallized before use. The a bases (Eastman Kodak) were purified by standard methods9 and distilled before use. The nonhydrogen bonding solvent used was n-heptane (E. Rlerck) which showed cutoff at 220 mp. The details of spectral measurements made on a Hilger uv spectrophotometer were same as described previously.8
Results and Discussion The a-a* band of a-naphthylamine in n-heptane at 318 mp undergoes a red shift to 322 mp in the P bases. Figure 1 shows the absorption spectra of a-naphthyl amine in n-heptane and in mesitylene. (1) (a) R. West, J . Amer. Chem. Sac., 81, 1614 (1959); (b) W. Beckering, J . Phys. Chem., 65, 206 (1961); (c) M. Oki and H. Iwamura, J . Amer. Chem. Sac., 89, 567 (1967). (2) P . J. Krueger and H. D. Mette, Can. J . Chem., 42, 288 (1964). (3) B. Ghosh and 9 . Basu, Trans. Faraday Soc., 61, 2097 (1965). (4) M. R. Basila, E. L. Saier, andL. R. Cousins, J . Amer. Chem. Soc.,
87, 1665 (1965). (5) (a) Z, Yoshida and E. 0. Sawa, ibid., 87, 1467 (1965) ; 88, 4019 (1966); (b) Z. Yoshida and N. Ishibe, Bull. Chem. Sac. Jap., 42, 3254 (1969). (6) B. Chakravortv and 8. Basu, J . Chim. Phys., 64, 950 (1967). (7) (a) 6. Nagakura and H. Baba, J . Amer. Chem. Sac., 74, 5693 (1952); (b) S. Suzuki and H. Baba, J . Chem. Phys., 35, 1118 (1961). (8) (a) S. K. De and S.R. Palit, J . Phys. Chem., 71, 444 (1967); (b) S. Mukherjee, S. R. Palit, and S. K. De, ibid., 74, 1389 (1970). (9) “Techniques of Organic Chemistry,” A . Weissberger, Ed., Vol. VII, Interscience, New York, N. Y., 1965.
.,
2405
NOTES 340 320
240
0'21 290
310
330
X,mp
-
350
!-
I
I 37*
Figure 1. Long wavelength absorption spectra of a-naphthylamine in I, n-heptane (A, 318 mp, e 3920) and in 11, mesitylene (A, 322 mp, e 8710).
Optical density measurements were made on mixtures of the proton donor and the different a bases at various concentrations of the latter a t the shifted peak (322 mp). The results were then examined for possible 1:l complex formation. I n the hydrogen bonding of a-naphthylamine (B) and T bases (A)
A + B ~ A B when [A] >> [B], the equilibrium constant may be calculated using the following equation3,*
where [A] and [B] are the concentrations of the a base and the proton donor, respectively, €1 and €0 are the extinction coefficients of the complexed and free anaphthylamine, respectively, K is the equilibrium constant, ;is the formal extinction coefficient of the solution, given by ; = D/[B]Z, where D is the measured optical density of the solution containing an initial concentration of [B] in moles per liter, and 1 is the path length in centimeters.
0
2
4
[AI
6
8
10
Figure 2. Plots of [A]/(: - eo) vs. [A] for different bases: I, benzene (7.94): 11, toluene ( 8 . 5 5 ) ; 111, ethylbenzene (7.81); IV, p-xylene (8.33); V, cumene (7.16); VI, chlorobenzene (7.81); VII, mesitylene (7.15). Numbers in parentheses indicate values of z in the ordinate where z X lo3 = l / [ B ] .
The observed linear plots of [A]/; - eo us. [A] (Figure 2 ) ) according to eq 1, show the formation of 1: 1 hydrogen-bonded complex between a-naphthylamine and the a bases. The equilibrium constants (Table I) increase with the increase in the number of alkyl groups in the series of aromatics studied. Possible steric effects due to substituted groups in the alkylbenzenes2 are absent in the present system of hydrogen bonding. Our results can be explained on the basis of inductive effects alone, where alkyl substitution increases the basicity of the a bases, while halogen substitution, as in chlorobenzene, decreases the same. Our findings are similar to the observations on 0-Ha . a i n t e r a c t i ~ n . l , ~ - ~
-
Table I : Equilibrium Constants for 1:1 Hydrogen-Bonded Complex Formation between a-Xaphthylamine and the A Bases at 25"
Base
Equilibrium constant, K , M -1
Chlorobenzene Benzene To1u en e Ethylbenzene Cumene p-Xylene Mesitylene
0.109 + 0.040 0 . 1 4 7 3 ~0.030 0 , 2 5 4 * 0.040 0.244=tO0.O50 0.608=tO0.O80 1.3003Z 0,100 2 . 2 2 0 i 0.150
Low-Energy Electron Radiolysis of Methane
by C. D. Finney and H, C. Maser* Department of Chemistry, Kansas State University, Manhattan, Kansas 66609 (Received JuLu 1.4, IQYO) Publication costs assisted b y U.S. Atomic Energy Commission
Several electron radiolysis studies have shown that information on mechanisms may result when the imThe Journal of Physical Chemistry, Vol, 76, N o . 16, 1971
